Dial light for telephone substation set



May 5, 1964 E. E. BAUMAN DIAL LIGHT Foa TELEPHONE suBsTATIoN SET 3Sheets-Sheet 1 Filed June 13. 1960 INVENTOR. EDWARD E. BAUMAN BYMf/f M@'M Mm ne w ...5on5 muufzu May 5, 1964 Filed June 13, 1960 E. E. BAUMAN3,132,211

DIAL LIGHT FOR TELEPHONE.' SUBSTATION SET 3 Sheets-Sheet 2 POLARITYPOWER SUPPLY CIRCUI T B SWITCH I3 g2 FIG. 2

INVENTOR. EDWARD E. BAUMAN May 5, 1954 E. E. BAUMAN 3,132,211

DIAL LIGHT Foa TELEPHONE sUBsTATIoN SET Filed June 13, 1960 3Sheets-Sheet 3 i' l l lf) 9' LL r l s u l E u i a' s n z l i' E I z ho qN INVENTOR, EDWARD E. BAUMAN United States Patent Office 3,132,211Patented May 5, 1964 3,132,211 DIAL LIGHT FOR TELEPHONE SUB- STATEONSETEdward E. Bauman, Galion, hio, assigner to North Electric Company,Galion, Ghia, a corporation of @hin Filed June 13, 1960, SerB No. 35,534Claims. (Cl. 179-81) The present invention relates to a novellight-producing mean-s ladapted for use with a telephone system, andspecifically to a novel 'generator circuit `for energizing asolid-state, light-producing media from the direct-current power on atelephone line.

There has been an increasing display of interest in the field for atelephone substation set which has a light-producing means whichprovides an improved form of illumination for the telephone `dial of asubstation instrument, whereby use of the instrument in areas having aminimum of, or no illumination will be greatly facilitated. The earlierstructures which were provided in the eld in `an attempt to satisfy suchdemands basically comprised means for mounting a lamp bulb adjacent thedial, land an extension cord for connecting such lamp to a 110 volt-alternating current source. Such arrangement, in addition to beingunsightly and subject to breakage, was of :limited utility in that itrequired location of lthe phone in reasonable proximity to 1l() voltagea1- ternating current source outlet. Such arrangement is furtherundesirable in that it requires the connection of 4110 volt alternatingcurrent power, with its attendant hazards, to the telephone substationset. In addition to .these various shortcomings, the nature of thelighting which was provided by the bulb yfor the dial was still far fromsatisfactory.

More recent developments have resulted in the provision of a solid stateelectroluminescent lighting media which by reason of its thin, compactconstruction can be placed on the substation set beneath the indiciawhich identify the di-al numerals, whereby an improved form of lightingis obtained, and the inherent problems eX- perienced with vacuum bulbs,including breakage, heat and space, are eliminated. One particularlysuccessful embodiment of such type lighting was set forth in theapplication of lEdward E. Bauman and Willard' A. Roberts, which wastiled on January VA4, 1960, land received Serial No. 194, and wasassigned to the assignee of this application.

Such an arrangement, as noted, has constituted a deiinite step forwardin the art of ydial lighting for substation sets. However, thearrangement there disclosed still requires a 110 volt A.C. source, andthe use of the device is at least partially restricted by suchrequirement. Further, as noted above, lthe connection of 110 volt A.C.source to a substation set is not considered particularly desirable inthe field, in that it introduces a possible hazard to the ltelephoneinstrument user as well as to the service personnel who must maintain.and install such units. There -is a need, therefore, for a telephonesubstation set which includes means for energizing a light producingmedia from the direct-current power on the telephone line to which thesubstation set is connected, and it is a primary object of the presentinventionto provide a new `and novel power source which lis operative togenerate without effecting an unreasonable s uch -form of power It is aparticular object drain on the line conductors.

of the invention .to provide a power source of such type which willenergize an electroluminescent cell from the low voltage direct currentpower on the telephone line conductors.

One of the basic poblems inherent in the excitation of a solid statedevice from the power on the telephone the telephone line conductorsline -is Ithe variable nature of the potential which occurs on the lineconductors at the substation instrument. That is, the potential on theline conductors is normally in the order of forty-eight volts when thesubstation handset is restored on the substation base (the on-hookcondition), and in the order of tive to eleven volts when the handset isremoved from the substation base (the off-hook condition). In certaintypes of commercially .available telephone substation sets, thepotential between the substation line conductors may even drop to zerovolts when the off-normal contacts close during the movement of the dialpreparatory to the transmission of the impulses, and as the dial pulsingcontacts open and close thereafter in the transmission of the impulses,the line potential varies between zero and forty-eight voltsrespectively at the rate of ten pulses per second. The novel powersource must therefore be capable of providing a steady energizingcurrent during the periods when the power available on the directcurrent telephone line is at the following Idifferent levels: (a) on-hoo48 volts direct current at 750 microamps current; (b) on-hook andringing 48 volts DC. plus and minus 100` volts ringing voltagesuperimposed; (c) oifhook-five to eleven Volts direct current at 20milli-amps maximum current; (d) off-hook dialingvoltage variationsbetween zero and forty-eight volts at ten pulses per second; (e) reversepolarity which occurs as the result of a steady, substantially constantpower -output for the lightemitting media independent of variation inthe supply potential for the circuit.

It is a further object of the present invention to provide a powersource which is operable in such manner at a low order of currentcompared to known lighting devices as connected to the variablepotential source of a conventional telephone line, whereby a largenumber of such devices may be coupled to the line without eiecting heavyloading of the system.

It is still another object of the invention to provide a novel sourcemeans which -is operative in such manner without resulting in noisyinterference on the line, or varying the quality of communicationtransmission media which are eifected over .the line conductors, oradversely affecting signalling.

In cer-tain uses and applications, in the home of the subscriber, it isfrequently ydesirable that the light be somewhat soft so as not to beoffensive when the unit is not in use, while yet providing a light ofsubstantially increased intensity when the receiver lis removed from thesubstation preparatory to a dialing operation, and it is a furtherobject of the invention to provide a power source which is operative toautomatically provide the diiferen-t levels of power output in thedifferent conditions of use of the substation set.

A particular feature of the invention is the manner in which the powersource which is adapted to energize a solid state light material fromthe direct-current of permits the use of the arrangement in theillumination of other forms of display media in areas in whichalternating current may not be readily available. tion to That is, thenovel source, in addibeing useful in illuminating the telephone dial,

t maybe valso used in the illumination of display media,

such as instruction signs, advertisingl displays, signal lamps,telephone directory illuminating lights, and many other types oflighting media, without requiring the 1ocation of the display mediaadjacent a volt alternating current source. Such arrangements areparticularly adapted for use in roadside paystation booths which havebeen heretofore somewhat limited in use by reason of the absence of 110volt A.C. source, or alternatively by reason of the expense involved inextending a 110 volt A.C. source to the booth atrthe location desired.The novel power supply circuit provides suliicient current to provideillumination for installations of such type, and therefore permits theuse of such booths at a greatly increased number of field locations.

The foregoing obiects, advantages and features of the invention will beapparent with the consideration of the following description anddrawings which disclose the embodiments of the invention, and in which:

FIGURE 1 is a schematic illustration of the novel power supply circuitof the disclosure as connected to a telephone line to effect theenergization of a solid state lighting device for the dial of one knownform of substation set;

FIGURE la is a schematic showing of the modified circuitry of a secondwell-known form of commercially available telephone substation set withwhich the novel device is used; and

FlGURES 2 and 3 are schematic showings for further novel embodiments ofthe power supply circuit for energizing a light-producing media.

General Description The novel power energizing circuits of the inventionare particularly adapted for use in energizing a lightemitting media fora dial and in the disclosed embodiments, are operative to energize anelectroluminescent light cell of the` type set forth in the aboveidentified patent to Bauman et al., wherein an annularelectroluminescent cell is disposed beneath the indicia carrier memberwhich is located about the periphery of the substation dial for thepurpose of identifying the dial holes. The electroluminescent cell asenergized by an alternating current source of power, provides apleasant, soft light output for the dial, a particularly satisfactorylight output having been experienced with the application of a powersource thereto having apotential in the order of between 50 and 1GOvolts at a frequency of approximately 250 cycles.

The power circuits of the invention are basically comprised of solidstate switching equipment including a transformer coil and semiconductorswitching members which are mounted within the confines of thesubstation housing. The input terminals for the power circuit areconnected to the subscriber line conductors and the circuit is energizedby the direct-current potential thereon for at least the periods thesubstation is not inuse. As shown hereinafter, the period ofenergization of the circuit by the direct-current line potentialvariesin different embodiments. In each arrangement, however, the powercircuit is operative as thus energized togenerate an alternating currentpotential for the electroluminescent cell.

According tofone feature of the invention, the disclosed embodiments ofthe novel power circuit are operative to energize the electroluminescentcell to provide a lightof a reduced intensity during the periodl thatthe receiver is on the substation base, or in the on-hook condition, anda light output of au increased value when the receiver is removed fromthe substation base, or in the off-hook condition, whereby a brighterlight output is obtained during the period of dialling and a reducedoutput is provided when the substation is not in use.

on a telephone substation set,

Power Supply With Charging,Circuit for Battery Polental Storage MeansWith reference to FIGURE the novel power supply circuit 1, afirstembodiment of S for a substation instrument includes inputterrninals 13,l5 for connecting the power supply circuit across the ringer circuit forthe substation set, and across the subscriber line conductors L, L2.Output terminals 35, 39 for the power supply ciri cuit are connectedover conductor pair 51 to the terminals 50 for an electroluminescentcell 14 which is mounted to illuminate the dial of a substation set asshown in the above-identified application.

Power supply circuit 8 basically comprises a lter circuit which isoperative to couple the direct-current on the line conductors L1, L2over a polarity switch 2t) to a power circuit 3d. Filter circuit 16 isoperative to block the ringing alternating current on the line from thepower circuit 30, and the polarity switch 20 is connected to provideenabling potential to the power circuit 39 regardless of the polarity ofthe direct-current voltage on the line conductors L1, L2 respectively.That is, conductor L1 may be positive and conductor LZ may be negative,or alternatively conductor Ll may be negative and conductor L2 may bepositive, and the polarity circuit Ztl will in either event couplepositive potential to the positive bus and negative potential to thenegative bus for the power circuit 30.

. The power circuit 30 which is energized by the potential on thepositive and negative buses basically comprises a transistor invertercircuit 21 including an oscillator circuit for converting thedirect-current voltage of the telephone line to an alternating currentof a value which effects the energization of the electroluminescent cell14 to provide the desired light intensity, the level of the light outputbeing adjustable in different conditions of the substation instrument.That is, the output of the inverter circuit 21 as coupled to theelectroluminescent cell 14 is controlled by the position of the hookswitch on the telephone substation set, the hook switch includingcontact means which connect one set of windings in the oscillatorcircuit when the substation is not inruse, and a second set of windingsin the oscillator circuit when the hook switch is operated preparatoryto a ktalking operation, whereby the signal output of the oscillatormeans and the light output of the electroluminescent cell is varied in amanner which results in a comparatively soft light during the on-hookcondition and a light output of increased Vintensity when the receiveris in the off-hook condition. A resistor 53 controlled by a knob in thesubstation housing permits further adjustment of the light output of thecell by thersubscriber in either condition.

Y The power circuit 3h also includes a potential storage means, such asa small nickel cadmium battery 69 in FlGURE 1, which is used to energizethe inverter circuit 21 when the substation is in the ott-hookcondition, and a charging circuit, such as circuit `22 in FIGURE l,which is energized by the potential on the line during on-hook conditionto charge the potential storage device 69 of the power supply circuit.As shown in more detail hereinafter, the potential storage means 69 atcertain times also provides a stabilizing potential for the invertercircuit 21 S pacific Description With reference to FIGURE 1, the novelpower supply circuit 8 includes a pair of input terminals 13, 15 forconnecting the power supply circuit 8 and the ringer circuit lil acrossthe line conductors Ll, L2 of the substation instrument. As shownthereat,y a conventional ringer circuit ltt may comprise a ringer device11 connected in series with capacitor 12 and bridged across lineconductors L1, L2. The input terminals 13 and 15 for the power circuitBtl are Vconnected to the line conductors L1, L2 in advance of theconnections of the line conductors L1, L2 to the substation transmitterandreceiver components 80. The substation components 80 are well knownin the art, and are therefore only briey identified hereat.

vat the rate of ten i capacitor 91 and to polarity switch 20, theimpedance choke behard of hearing,

`result in a pulsating variation of the light relectroluminescent lamp14, and

`manner' between the one side of ative bus for the lpower circuit 313;

connected between the negative bus andthe second side by resistor 85 andcapacitor 84, which are connected in series with rectifier diodes ofdial Contacts 33 responsive to moving of the dial by the subscriber totransmit pulses over the conductors L1, L2

pulses per second. u

An induction coil S7, including primary windings 87P, SSP, secondarywinding 89S, and tertiary winding 90T, a sidetone balancing circuit, atransmitter element 95 and a receiver element 98 are also connected tothe line conductors L1 and L2 in a conventional pattern. Briefly,primary winding 87P is connected to conductor L1, and primary windingSSP is connected to conductor L2, and transmitter 95 is connected inseries withresistor 96 across the primary windings S'7P, SSP. Receiver98 which is shunted by rectifier 97 and off-normal contacts 99, 100, isconnected between primary winding 87P and over tertiary winding 90T ofinductance coil S7, capacitor 91, and the secondary winding 89S to theprimary winding SSP of the induction coil 87;r A sidetone balancecircuit including rectiers 92 and capacitor 93 connected in parallelwith each other and resistor 94 are connected across the primary windingS'P of inductance coil87. The connection and operation of the substationtransformer, receiver and inductance coil components are well known inthe art, and'further description thereof is not required. f

The filter circuit 16 for the power supplycircuit 8 comprises choke coil18 and capacitor 19 connected in series between input terminals 13 and15 which are `connectedtoiconductors L1, L2 respectively. Filter circuit16 couples the direct current on the line conductors L1,

l L2 to the polarity switch 20 and blocks alternating curfrom enteringthe 18 blocking alternating current from the switch 20, and thecapacitor 12 shunting any small amounts of alternating current rents onthe line conductors L1, L2

86 to conductor L2, such circuit being V`primarily effective withopening and closingV ,y ing the extension of a connection.

which may pass choke 18 to the opposite line conductor L2. Thealternating current components on the conductors L1, L2 may, of course,be the conventional ringing voice currents or transients subscribertelephone line.

In certain embodiments, it may be desirable to provide a visualdisplayof incoming signals as well as (or in lieu of) the conventionalaudible ringing signals.. Such arrangements are particularly Vuseful tosubscribers who may or to subscribers who may find the noise of theconventional ringing device objectionable. In such embodiments, it isonly necessary to provide a coupling between the line conductors L1, L2and the power supply circuit 8 which is suiciently loose to permit theringing signals to reach the power supply circuit 8.

.Such coupling is achieved by providing a choke 18 and capacitor19.which are sufficiently low in value as to permit the leakage of suchcurrents and thereby a variation of the potential supplied to theinverter circuit. Variation in the supply of the powerto the invertercircuit 21 as a result of ringing current (100 volts land v-`) beingcoupled to the substation in the intensity of the v thereby a visualsignalling effect which indicates an incoming call.

Polarity/*switch 20 comprising rectifier diodes 2 3-26 is connectedacross Acapacitor 19 of the filter circuit 16, rectifier 24 beingconnected between Athe one side of the capacitor 19 and the positive bus(-4-) for the power circuit 30; rectier 23 being connected in anoppositely poled rectilier 25 being of capacitor 19with the polarity ofrectifier 23; and rectier 26 being connected between the second side ofcapacitor 19 and the positive bus with the polarity of rectifier 24. Theoutput terminals of the polarity switch 2t) provides a potential of theVpolarity indicatedin FIGURE 1 which normally occur on aV capacitor 19and the negon-hook condition, will to the positive and negative busesfor the power circuit 30 regardless of the polarity of the directcurrent as coupled to conductors L1, L2. The polarity circuit thuspermits the use of the power source with the telephone subscriber lineregardless of the polarity of the telephone line conductors.

In the field, for example, the polarity of the telephone line conductorswhich are used in the extension of cells to different' exchanges mayvary. Further, in switchboards' which use reverse battery supervision.the polarity of the potential on the line conductor will be reverseddur- The polarity switch is included in the circuitry to provide commonsupply buses of iixed polarities for the power circuit independent ofsuch variations, whereby changes and variations of the polarity of theline conductors will not affect the operation of the power circuit 30. vbasically comprises inverter cir- The power circuit 3i) cuit 21, battery69, battery charger circuit 22, hook switch contacts i6-48, 49, 52, 52A,557-57, of the telephone substation set, and output terminals 35, 39which are connected by conductors 51 to the input terminals 50 for theelectroluminescent cell 14. Inverter circuit 21 basically comprises atransformer 31 ,having primary winding 32 and secondary windings 33, 34anda pair of transistor members T1 and T2 which are coupled to theprimary and secondary windings of transformer 31. Switch hook contacts49-52, 5S, 56 are transistor members T1, T2 to different segments of thetransformer 31 to vary the output signals of the inverter circuit 21 inaccordance with the on-hook, off-hook conditions of the telephonesubstation device, and also to vary the source of potential for withus'e of the substation instrument.

Primary winding 32 on 35-39, taps 35 and 39 being end taps, taps 36, 38being intermediate taps, and tap 37 being a center tap for the vprimarywinding. Secondary winding 33 includes taps 40-42, tap 41 being thecenter tap for the secondary winding 33; and secondary winding 34includes taps 43-45, tap 44 being the centerftap for secondary winding44. The coil of the transformer 31 is of a square loop saturablematerial, such as is commercially available in the field as Hi Mu 80.The polarity of the windings is as indicated by the dots shownin thedrawing adjacent thereto.

More specically, transistor T1 comprises a collector element 61, a baseelement 62, and an emitter element 63, collector element 61 beingconnected over switchhook contacts 52, 52a, resistor 54, the portion ofthe rtransformer primary winding 32 which extends between taps 35 and 37and switch-hook contacts 47-46 -to the negative supply bus of thepolarity switch 20,*it being apparent that with operation of theswitch-rook to effect the opening of contacts 52, 52a, and the closureof contacts 49, 52, collector element 61 of transistor T1 will beconnected to terminal 36V on the primary winding of transformer 31 toprovide an increased signal output as Y described more fullyhereinafter. Base'62 of transistor Tl is connected current limitingresistor 59, the portion of the secondary winding 33 which 40, 41 to avoltage divider 67, 68 whichis connected across a nickel-cadmium batterycell 69, the point of connection being such that the base 62 has anegative starting bias with respect to emitter 63 which is connecteddirectly to the positive supply bus of the polarityV switch 2t).

Transistor T2 comprises a collector element 64, base element 65 andVemitter element 66. Collector .element 64 is connected over'switch-hookelements 56, 57, and

. current limiting resistor S8 through the portion of the operative tocouple the the inver-ter circuit 21 l transformer 31 includes taps.

extendsv between taps contacts 56, 57 and close contacts 55, 56 thecollector will be connected to tap 38 ofthe primary winding 32 toprovide an increased signal output as more fully described hereinafter.Base 65 is connected over current limiting resistor 60 and the portionof the secondary winding 33 which extends between taps 42 and 41 to acommon point of connection on voltage divider V67, 68 Withthe base 62 oftransistorA T1. Emitter 66 of transistor T2 is connected directly to thepositive supply bus, whereby the connection of the base 65 to the morenegative point on the voltage divider 67, 68 provides the base with thenecessary negative bias with respect to the emitter 66.

The output of collectors 61, 64 of transistors T1, T2 respectively, iscoupled over terminals 35, 39 and adjustable resistor 53 and contacts 51to the terminal 50 for the electroluminescent cell 14. As shownhereinafter, with the substation not in use the inverter circuit 21 isoperated by the direct-current battery potential on line conductorsLl-LZ to provide an alternating current signal output to energizeelectrolurninescent cell 14, and with the substation in use, thepotential storage means 69 are connected to energize the invertercircuit 21 in the excitation of the electroluminescent cell 14. Y

A charging circuit 22 for potential storage means 69 is connected to thesecondary winding 34 of transformer 31 for energization during theperiods in which the telephone ksubstation set is not in use (in theon-hook condition). During such periods as the substation is in use bythe subscriber, the inverter circuit 21 and the charging circuit 22 aredisconnected from the telephone line, and the battery is connected as asource of power for the inverter circuit 21. y f

More specifically, the charger circuit 22 comprises a air of transistorsT3, T4 which are connected in a controlled full wave rectifier circuit,the transistor T3 including collector element 70, base element 71,emitter element 72, and transistor 74 including collector element 75,base element 76 and emitter element 77, respectively. Collector element76 of transistor T3 is connected over the portion of the secondarywinding 34 which extends between taps 43, 44 to the positive bus, andcollector 75 of transistor T4 is connected over the portion of thesecondary winding 34 which extends between taps 45, 44 to the positivebus. Emitters 72, 77 of transistor T3, T4, respectively, are connectedover a common resistor 7 8 to the negative terminal of potential storagemeans 69, and the base elements 71, 76, are connected over resistors 73,74, respectively, to switch-hook contacts 47, 46 and the negative bus.In that the transistors T3, T4 are connected between the opposite endsof the secondary winding 43, 45 and the center tap 44, voltages ofopposite polarity will be coupled to the collectors 71, 75 duringalternate half cycles of the signal output of the inverter circuit, andthe transistors will operate in the manner of a full wave rectifier tocouple the charging circuit to the potential storage means 69. Duringthe period that the substation is in the off-hook condition theconnection as shown provides a bias at the junction of resistors 73, 74which is connected over hook-switch contacts 47, 48 and returned overresistor 7 to the emitter of transistors T3, T4, whereby the transistorsT3, T4 will not be conductive.

It is -apparent that other forms of transistor switching arrangementsmay be used to complete the charging circuit for vthe potential storagemeans Without departing from the spirit of the invention.

Operation of Power Supply Circuit i In operation, the novel power supplysource effects excitation of the electroluminescent cell to provide alight output of a constant nature, the intensity of the light outputbeing automatically varied for different conditions of use. That is,during the period that the Vsubstation is not in use, the switch-hookcontacts are in the on-hook condition and the light is of a minimumintensity.y With set preparatory to vide an energizing circuit tooperation of the switch-hookA contacts on the substation use by thesubscriber, the intensity of the light output is substantiallyincreased.

In more detail, with; the switch-hook contacts in the on-hook condition(receiver on the substation set in structures of the type shown in theabove-identified application); contacts46, 47 areclosed and contacts 47,48 are opened, contacts 52, 52a and 56, 57 are closed, contacts 49, 52and'55, 56 are opened, and contacts 81, 82 are opened. Assuming aconventional telephone system V(and a small drop of potential whichoccurs across choke 18 and diodes 23-26), the voltage across thepositive and negative buses for the inverter circuit 2l will beapproximately 48 Volts when the telephone substation is in the on-hookcondition. In such condition, transistors T1 and T2 in inverter circuit21 are energized by the 48 volt potential on the line conductors L1, L2to provide an energizing potential overrconductors 51 to theelectroluminescent cell 14. With reference to the inverter circuit 21,emitter 63 of transistor T1 is directly connected to the common positivebus, and collector 61 is connected over switch-hook elements 52, 52a,current limiting resistor 54, to tap 35Y and the portion of thetransformer primary winding 32 which extends between taps 35, and 37 andswitch-hook elements 47-46 to the negative bus, and the base 62 isconnected over current limiting resistor 59 to tap 40, and the portionof the secondary winding 33 which extends between taps 40 and 41 to apoint on the voltagedivider 67, 68 which biasses the base 62 negativewith respect to the emitterv 63 to thereby protransistor T1 therefor.

Transistor T Z of the inverter circuit 21 isbiassed in a similar manner.That is, emitter 66 is connected to the positive bus', collector 64 isconnected over contacts 56, 57, current limiting resistor 5S to tap 39,the portion of the transformer winding 32 which extends between the taps39 and 37, and over switch hook contacts 47, 46 to the negative bus; andthe base 65 of transistor T2 is connected over current limiting resistor6i) to tap 40 and the portion of the secondary Vwinding 33 which extendsbetween taps 42 and 41`to a point on the voltage divider 67, 68 which isnegative with respect to the potential which is coupled to emitter 66.

It is apparent that with the telephone in the on-hoolr condition,emitters 63, 66 are positive with respect to the bases 62, 65respectively, and the emitter-base paths are biassed in the forwarddirection and the collector-base paths are biassed in the reversedirection, whereby both transistors T1 and T2 are biassed for operationaccording to'. conventional common emitter configurations. In that thebiasing of both transistors T1,y T2 results in a bistable condition, inaccordance with well-known operating concepts, one transistor of thepair will conduct before the-second transistor, and the transistors T1and T2 will conduct alternately to saturate the core of the transformer31 -irst in one direction and then in the otherA direction, to therebyprovide an essentially square wave output attterminals 35, 39 atapproximately 300 cycles per second. Y

In more detail, as one of the transistors T1, T2 is energized (andassuming base 62 of transistor T1 is going negative), current will flowover the emitter collector path 63, 61, contacts 52, 52a, currentlimiting resistor 54, the Winding between taps 35, 37 on transformer 31,and contacts 47,46 to negative'potential. Y

By regenerative action in transformer 31, the changing potential iscoupled over the secondary winding 33 of transformer 31, and the portionof the changing potential which appears across taps 40, 41- drives thebase 62 of transistor T1 almost instantaneously to its most negativepotential relative to emitter 63 to control transistor T1 to conduct.The same transformer action effects coupling of a changing potentialover the portion of the winding 41,142 to the base 65 of'transistor T2to bias the base to its most positive potential relative to the emitr,vente l taneously value of l lator continues in a repetitive ter 66 tothereby drive transistor T2 to cut off. Such action occurs in anextremely short time interval, and re- Vsults in a rapid switchingperiod.

An increasing current now flows through the emittercollector path 63, 61of transistor T1 and the portion of the primary winding which extendsbetween taps 355-37 during the period of conductivity of transistor Tluntil the core of transformer 31 becomes saturated, whereupon a rapidcurrent rise occurs in the portion of the winding which extends betweentapst35, 37. As the emitter-collector `current flow in transistor Tlexceeds the value which the base current times beta will permit as aresult As the potential of base'62 approaches the value of the potentialor" emitter 63, transistor Tl. is cut oii, and the base continues tobecome more positive toumaintain the transistor in such state.Simultaneously, as the potential ofthe base 55 of transistor "F2-becomesmore negative than the emitter 66, transistor T2 conducts and currentflows from the positive bus over the emitter-collector path 66, (5f-ivof transistor T2 and over contacts S6, 57, current limiting resistor 58,the portion of the transformer v Winding 39, 37 and contacts 47, d tothe negative supply bus.

The changing potential which appears in the Winding 39, 37 results, bytransformer action, in a changing poof the ytransformer 4l, and the base65 of transistor T2 is driven almost instanto its most negativepotential, and the base 62 of transistor Tl is driven almostinstantaneously to its most positive potential. The iirst half cycle ofthe wave- Vform output of the oscillatoncircuit has now been generatedand the leading edge of the second half cycle has been initiated.Thereupon, the increasing current emitter-collector path of transistorT2 flow through the and primary winding 39-37 of transmitterSli-continues until the core of' transformer 31 becomes saturated in thereverse sense,

t and rapid current rise occurs in Winding 39-37. Such action occursduring the period of generation of the seci ond half cycle of the outputwaveform.

As .the emitter-collector current of transistor T2 exceeds the valuewhich the base 'current times beta will support as a result of the rapidcurrent rise in transformer winding 39, 37, transistor T2trnoves out ofsaturation and an abruptly increasing potential occurs across theemitter-collector path with Va resultant-i decreasing potential acrosswinding segment 39, 37. As a result of the changing potential in'theprimary windingof transformer` 3l,

and the resultant change in potential inthe secondary winding of`transformer 31, `base 62 of transistor T1 is driven negative and base 65of transistor T2 is driven positive. As the potential of the base 65approaches the the potential of the emitter 66, transistor T2 is drivento positive. Simultaneously as the of transistor T l becomes more 63transistor `T1 conducts to initiate al subsequent cycle.

The alternate operation of the transistors as-an` osciltially square`wave waveforms at 300 cycles per-second and couples such output to taps3 5 and 39 and over conductors 51 to the Velectroluminescent cell M toenergize same inthe illumination of the dial of the telephoneinstrument. f control (not shown) which vextends to the exterior of thecutolhand the base continues to become more n potential of the base 462negative than the emitterV manner to provide essen- Y t emittercollector'path 77, 75

telephone substation housing permits manual adjustment of thealternating currentin the output circuit of the inverter circuit 2l andthereby the intensity of the illumination provided by theelectroluminescent cell i4.

During the period in which the receiver `is restored on the substationbase (on-hook condition), and the inverter circuit 2 is energized by thepotential on the line conductors to provide the necessary power forilluminating electroluminescent cellll, a potential storage means(rechargeable nickel-cadmium cell 69 in the illustrated embodirnent) issubjected to a continual charging current by charger circuit 22.1 Asshown in FIGURE l, transistors T3 and T4 of charge circuit'ZZ areconnected across the secondary winding 34 of transformer 31, and areenergized in the manner of a full Wave rectiiier to provide a continuoussupply of charging current to the battery cell 69 More specifically, thebase elements 7l and 76, respectively, are connected over resistors 73and 74 and. contacts 47, 46 to the, negative bus; collectors 70 and 75are connected over taps 43 and i5 respectively to the secondarywindingli of transformer positive bus for the inverterV circuit; areconnected over resistor 7S to the negative terminal of the battery e9which is negative relative to the common positive bus.

During the period of energization of inverter circuit 21 by the linepotential (the ori-hook condition), the square wave signal output of theinverter circuit also appears across the secondary Winding 34- oftransformer 31 and at the collectors 76, 75 of ransistors T3, T4 whichare connected to opposite ends of transformerfwinding 34. Voltages ofopposite polarity will therefore appear at the collectors 70, 75 duringsuccessive half cycles of the inverter circuit. As thepotential at tap43 is negative, and the potential at tap 45 is positive, transistor T3conducts and transistor T4 is cut off. During such half cycle, chargingcurrent is coupled to battery 69 over it over the common positive bus,battery 69, resistor 7S, the emitter-collector` path 72,

and emitters 72, 7'7

winding which extends between taps 43 and 44, tap 44. As the potentialat tap 45 becomes negative, and the potential tap 43 is positive duringAthe next half cycle of the inverter signal output, transistor T4conducts and transistor T3 is cut oi. During such half cycle, battery 69is charged over the path which extends from tap 44 to the common bus,and over battery 69, resistor 7S and the of transistor T4 to tap A55,and the portion of the secondary winding which extends from tap 45 totap 424. The battery being of the nickelcadmium type cannot beovercharged, and automatically terminates the charging operation as itsfull capacity is reached.

it will be apparent that with the load of the battery charging circuit22 onV the transformer El during the onhook condition of the substation(when the substation is not in use), theresultant load of the batterycharger will assists in the reduction of the of cell i4. Currentlimiting resistors 54.1, S8` in the output circuits of the oscillatortransistors Tl, T2 in addition to preventing transistors Tl, T2 fromdrawing too much current, are also operative to effect a reduction inthe power coupled to the electroluminescent cell, and thereby areduction' in the light intensity.

Operation 0f Power Circuit With Substatioiz in Off-Hook Condition Asindicated heretofore, as the subscriber effects operation ofthesubstation hoo r-switch preparatory to dialing A variable resistor 53having an adjustable the subscriber (or answering an incoming call), theintensity of the light output of the electroluminescent cell isincreased to provide a brighter source of illumination for the dial.

intensity ofthe light output As the hook-switch contacts are operated insuch manner, contacts 46, 47 are opened and contacts 47, 48 are closed;contacts 52, 52a are opened and contacts 52, 49 are closed', contacts57, 56 are opened and contacts 56, 55 are'closed, and contacts 8l, 82.are closed.

As contacts 8l, 82 are closed, a direct-current loop is extended fromconductor Ll over various paths in the operating elements of thesubstation set (transmitter 95, receiver 98, sidetone balancing circuit92, 93, 94, induction coil 87, dial contacts 83, etc.), to the lineconductor L2. The voltage across conductors Ll, L2 at the substation atsuch time in certain installations will drop to a value of between S-llvolts, the value of the voltage being variable with the resistance ofthe telephone line from the central office and other installationcriteria. Thus, with the removal'of the handset from the substationbase, the available voltage is reduced from 48 volts to 5-l1 volts.However, it is at this time that an increased power output is requiredof the inverter circuit 21.

Switch-hook contacts 46, 47, as now opened, interrupt the connection ofthe inverter circuit 21 tothe line conductors Ll, L2, and switch-hookcontacts 48, 47, as now closed, couple the inverter circuit 21 to thebattery 69, the switch-hook contacts 47, 48 connecting the center tap 37on transformer 31 to the negative terminal of battery 69. The emittercircuits 63, 66 are connected as the positive terminal of battery 68.

Simultaneously switch-hook contacts 52, 52a, open to interrupt theconnection of the collector 61 of transistor Tl to transformer tap 3S,and contacts 52., 49 close to connect the collector 61 to transformertap 36. In a similar manner switch-hook contacts 56, 57 open tointerrupt the connection of collector 64 of transistor T2 to transformertap 39, and contacts 55, 56 close to connect collector 64 of transistorT 2 to tap 38 of transformer 3l. Taps 36 and 38 are located at a pointon the primary winding 32 of transformer 3l to effect a substantialincrease in the power output of the transistors Tl, T2 to theelectroluminescent cell 14. The change of the connection of thecollectors 61, 64 to taps 36, 38 in lieu of taps 3S, 39 also increasesthe volts/ turn ratio, and thereby the frequency output of theoscillator circuit to increase the light output of theelectroluminescent cell. The voltage between the terminals 35 and 36 andalso between terminals 38 and 39 is now effected by auto-transformeraction. i

It will be apparent that with contacts 46, 47 open the inverter circuitis completely disconnected from the line conductors L1, L2 so that the300 cycle output of inverter 21 cannot be coupled over the lineconductors to the receiver 98 of the substation unit during talking.

Transistors T1, T Z oscillate in the inverter'circuit 2l in the mannerof the previous description. The supply voltage coupled to tap 37 bybattery 69 however is of a substantially lower value than the voltagecoupled thereto when the inverter circuit is connected to lineconductors Ll, L2. That is, as contacts 46, 47 open, and contacts 47, 48close, the transformer primary winding tap 37 is transferred from theline conductors (48 volts negative) to the negative terminal of battery69 (3.5 volts negative), and the base elements 71 and 76 for transistorsT3, T4 are also simultaneously switched from the 48 volt negative bus tothe'3.5 volt negative terminal of battery 69. Additionally, transformerturns 36, 37 are now connected in the collector circuit of transistorTl, and transformer turns 37, 38 are now connected in the collectorcircuit of transistor T2. In that collectors 61, 64 of transistors Tl,T2 are operating at a lower value, voltage current limiting resistors,such as 54, 58 are not required. v

With the bases and emitters of transistors T3, T4 in charging circuit22. at essentially the same potential, transistors T 3 and T4 are biasedto cut off, and a high resistance obtains in the emitter-collector pathsthereof to prevent the battery from drawing charging current over sec-12 ondary "winding 34 during the period that the inverter circuit 21 isenergized by the battery source.

A funther feature of the novel power supply circuit is .the manner inwhich the connection of substation sets including the power supply to Iaparty line are operative to provide a visual signal to the subscriberson the line which indicate that the line is in use. That is, in theevent that one Iof the subscribers on the party places the line in useby operating the hook-switch .contacts preparatory to the establishmentof an :outgoing call cr alternatively in answering an incoming call, thebattery voltage :across the line conductors L1, L2 will be reduced fromthe normal on-hook value of forty-eight volts,` to the off-hook value offive-eleven volts. In that such value cf voltage is insufficient tomaintain the inverter circuits 21 operative in each of the othersubstations which are connected to the same party line (and which are inthe on-hook condition), the power output of fthe inverter circuit 21 atthe substations on the party line which are not in use will be reducedsufficiently to extinguish the electrolurninescent cells thereat andthereby indicate to the other subscribers on the party line that theline is in use. Such arrangement permits .the provision and use cfpar-ty line installations rwithout the normal :aggriav-ations whichoccur when parties desiring to use lthe line must necessarily hrstlisten in to ascertain if the line -is in use, :and must repeatedlytherea ter listen i VV to determine if the parties using the line havecompleted their conversation. Such source of annoyance to the users :ofthe line and the subscriber awaiting Ithe opportunity to use the line isthereby avoided.

Specific Circuit Arrangement Diod 23, 24, Z5, 26 IN 2069 silicon.Resistors 54 and 58 27,000 ohms. Resistors 59 and 60 1,000 ohms.Resistor 67 `1,500 ohms. Resistor 68 68,00() chrns. Resistor 78` 220ohms.

., Resistors 73 and 74 4,500,000 ohms. Rhcostat y1,000,000 ohms.Transistors Tl and TZ RCA 2N398. Transistors T3 and T4 2Nl375.

l rTransformer:

EI laminations identified as 187 by the trade, of Hi Mu material Turnsbetween tapsk35-36=2670 turns of #43 enamel wire `:i6-T17 :220 turns of#43 enamel Iwire 37438=220 turns of #43 enamel wire SaS-39.12670 turnsof #43 enamel rwire t0-421:15() turns of #43 enamel wire 414421:- turnsof #43 enamel wire A13-44:50() turns `of #43 enamel wire 4445i=500 turnsof #43 enamel wire Condenser 2210 rnfd. nonpolarized Filter choke 214-23hennies Battery 69-nickel-cadmium battery- 150 ma. hours ratting-3 cellsat 1.35 volts The yabove identified values are representative of thecomponents utilized in a I bstation set in which the line conductorpotential is at 48 volts when the substation set is in the Yon-hookcondition; the line conductor potential is 5-11 volts in the olf-hookcondition, land the voltage during dialing may drop to zero volts.M-anifestly, if the device is used in installations in which thesevalues differ materially, corresponding changes in the values of atleast certain of the components will be effected.

' tion relating to the arrangement of FIGURE l.

t3 Power Supply Circuit for Charging Potential Means During O-HookConditionv further embodiment of the novel power supply circuit 8 isshown in FIGURE 2', the portions of the circuit of FIGURE l which aresimi-lar not being shown in detail to simplify the description of thefeatures of the ernbodiment shown in FIG `RE 2. Y

As there show-n, the power supplycircuit 8 includes amore simplifiedform of charging circuit tor the potential storage means 69, thecharging circuit including la basesbias resistcriiil, a series connectedlamp 163, a rectier 164 connected in parallel with lamp |163, 'and a ofswitch-hook contacts 47 and 41S tor connecting charging current ofdilerent magnitudes to the potential source means.' Switch-hook contacts47 and 48 are open lw'nen the substation is in the on-hook condition,:and are closed Storage of different charging currents between Ithenegative buses for the power supply circuit .-8 and the negativeterminal of the potential supply source :69. It is apparent that such larrangement eliminates the needgtor la second winding on transformer 31,and a charging circuit having switching components such transistors T3'and T4 in FIGURE 1`.

When the substation is not lin use (on-hook condition) anda 48 voltpotential is connected to the line conductors L1, L2, a trickle chargeis `coupled to battery cell 69 over a path which extendsfrom thenegative bus over resistor itil, lamp 163 and battery 69 to the positivebus for the power supply circuit Sto compensate ior the base-biascurrent which is rbeing dralwn lby .the oscillator circuit. The powersupply circuit otherwise operates in the manner of the arrangement shownin FIGURE l.

As the subscriber prepares to use thesubstation, and the substation ispl-aced lin the olf-hook condition, the switch hook contacts 47, 48 areclosed, and the potential on the conductors L1, L2 is coupled overswitch-hook contacts 47, 4S and lamp 166` to the potenti-al supplysource 69 to provide a charging current ofna substantially increasedvfalne thereto. Lamp 163 in the charging circuit operates 'as a currentregulator, and the constant voltage of battery 69 prevents the voltageacross the windings 36, 3-7, 317, 38 from increasing to .an amplitude ofunreasonable value. y Y

During the dialing operation (at which time the potential in circuit ofsome telephone 'substation sets may drop to zero volts see 'FIGURE la]the battery 69' lwill be operative to couple an energizing potential tothe inverter circuit 21 to maintain the output thereof constant, eventhough theI supply potential ywhich is normally coupled thereto by theline iconductors has dropped to zero volts. The energizing Icircuit forthe inverter circuit 2|1 now extends from the nega-tive terminal ofbattery 69 over rectifier 104 (which is conductive by reason of the factthat the negativeterminal .is now S-J/z volts more negative than thenegativeV bus which is .at zero volts) and over switch circuit contacts47, 48 to the center tap 37 to the primary winding. of transformer 311and the energizing circuitwor the inverter circuit 21 las set forth inthe descrip- Diode 23 prevents the low voltage on the line conductorfrom resulting in a dead short for the battery 69;

As the dial contacts open, the line voltage alternates circuit 2l in theevent that the potential on the line conwhen the substation is inthecitabook condition, lthe dif- Y ,ferent conditions of `operationeffecting the completion ductors L1 and LZ should drop below the normalvalue coupled to the inverter circuit 21 during dialing.

' Power Supply Circuit With Capacitor Potential Y Storage Means cludirigresistors 67, 63 when the substation is in the 011- hook condition(notin use). Switchhook contacts 47, 48 are open with the substation insuch condition, and the condenser 62 is therefore not normally connectedacross conductors L1, L2.

With roperation of the substation to the olf-hook condition, contacts47, 48 close and capacitor C2 is connectedacross the negative andpositive buses for the power supply circuit 8, and also also across thevoltage divider including resistance 67, 68, 68a.

When the substation is in the on-hook condition, the inverter circuit 21is energized by the power of the positive and negative buses, thepositive bus being connected to the'emitter elements for the transistorsT1, T2 and to one end of the voltage divider as comprised of resistances67, 68. The negative bias for the emitter base elements of thetransistors T1, T2 is obtained by reason of the connection of theresistances 67*68A of the voltage divider between the positive andnegative buses for the power supply circuitV 8,. The inverter circuit 21isoperative in the manner setf forth in the description above relativeto the lnverter circuit 21 in FIGURE 1.

the potential which is coupled thereto by the line conduc` tors L1, L2,whereby. a constant value potential is maintained in the supply circuitfor the inverter circuit 21, regardless of the condition of operation ofthe substation set.

The long time constant provided by the choke 18', and

f modifications and alterations asvrmay fall within the true spirit andscope ot" the invention.

What is claimed is: l: In ya power supply circuit adapted to be coupledto n e t' power on said voice communication lines to generatealternating current output signals of a value to energize saidelectroluminescent cell, and output means for coupling said alternatingcurrent signals to said electroluminescent cell.

2. In a power supply circuit adapted to be coupled to a direct-currentsource in a telephone system to provide an alternating current signaloutput to an electroluminescent cell comprising input means for couplingthe power supply circuit to the direct-current conductors of a telephoneline, an inverter circuit coupled to said input means operative togenerate alternating current output signals of a value to energize saidelectroluminescent cell, output means for coupling said alternatingcurrent signals to said electroluminescent cell, and potential storagemeans in said power supply circuit for supplying auxiliary power forenergizing said inverter circuit for. at least certain periods ofoperation of said inverter.

3. In a power supply circuit for use in a telephone substation setadapted to be coupled to the line conductors in a telephone system toprovide an alternating current signal output for energizing anelectroluminescent cell on the substation set comprising input means forcoupling the power supply circuit to said line conductors, an invertercircuit coupled to said input means operative to generatealternating-current output signals of a value to energize saidelectroluminescent cell, output means for coupling said alternatingcurrent signals to said electroluminescent cell, and switching meanscontrolled by the switch-hook on said substation set in one position toreduce the power output of said inverter circuit and in a secondposition to increase thepower output of Said inverter circuit tocorrespondingly vary the intensity 'of the light output of said cell. y'

4. A power supply circuit as set forth in claim 2 in which said inputmeans includes a fiiter circuit connected between said line conductorand said inverter circuit to block the passage of alternating currentcomponents On the line conductors from said inverter circuit. Y

5. A power supply circuit as set forth in claim k2y in which said inputmeans includes a first and a second input conductor for said invertercircuit, and a polarity switch including a rectifier bridge connected tothe line conductors to connect potential of one polarity to said firstconductor and a polarity of a second potential to the second conductorindependent ot the natureA of the connection of the two polarities tothe line conductors.

6. In a power supply circuit adapted to be coupled to a direct currentsource in a telephone system to provide an alternating current signalloutput to an electroluminescent cell comprising input means forcoupling the tothe conductors of a direct current telephone line, aninverter circuit coupled to said input means operative to generatealternating current output signals of a value to energizel saidelectroluminescent cell, including an oscillator circuit including afirst and a second semiconductor devicee`ach of which has an outputcircuit and at leastone element connected to its output circuit, atransformer member including a center tapped primary Vwinding includingmeans for connecting the center tap to one side of said source, and acenter tapped secondary winding means Yconnecting the center tap of thesecondary winding to the other side' of said source and the outputcircuits of different onesl of said semiconductors to diierent sides ofsaid centertap on said secondary winding, multiposition switch meansoperative in different positions to connect different :sections of saidprimary winding having a different-. turns/ volts ratio in the output'circuits of said semiconductor devices, means for connecting a controlelement of each of said semiconductor devices to said secondary Winding,the control elements of the different semiconductors'being connected toopposite sides of the center tap :ofthe secondary winding, and means forcoupling a further element of each semiconductor totsaid other side ofsaid power supply circuit l5 potential source to control thesemiconductor devices to operate as an oscillator circuit; and outputmeans for coupling the alternating current signal output of saidoscillator circuit to said electroluminescent cell.

7. In a power supply circuit adapted to be coupled to a direct-currentsource in a telephone system to provide an alternating current signaloutput to an electroluminescentcell comprising input means for couplingthe power supply circuit to the direct-current conductors of a telephoneline, an inverter circuit coupled to said input means operative togenerate alternating current output signals of a value to energize saidelectroluminescent cell, output means for coupling said alternatingcurrent signals to said electroluminescent cell, potential storage meansfor supplying auxiliary power to said inverter circuit, charging circuitmeans for said potential storage means, and means for conducting apotential obtained from said line conductors to said charging circuitmeans for said storage means.

8. A power supply circuit as set forth in claim 7 in which saidpotential storage means comprises a battery cell. Y

9. A power supply circuit as set forth in claim 7 in which saidpotential storage means comprises a capacitor device. Y

10. A power supply circuit as set forth in claim 7 in which saidcharging circuit means includes at least one semiconductor device, meansfor connecting said semiconductor in circuit with the potential storagemeans, and means for connecting a charging potential obtained from saidsource over `said semiconductor device to said potential storage means.Y l

ll. In a power supply circuit for use in a telephone substation setadapted to be coupled to the line conductors in a telephone systemltoprovide an alternating current signal output to an electroluminescentcell on the substation set comprising input means for coupling the powersupply circuit to said line conductors, an inverter circuit coupled tosaid input means operative to generate alternating current outputsignals of a value to energize said electroluminescent cell, outputmeans for coupling said alternating current signals to saidelectroluminescent celi, potential storage means in said power supplycircuit for supplying auxiliary power to said inverter circuit, acharging circuit for said potential storage means, and multipositionswitching means on said substation set operative in movement to oneposition to connect said chargingycircuit for energization by potentialobtained from said line conductors, and operative in movement toa'second position to vinterrupt the connection for the charging circuit.

l2. In a power supply circuit for use in a telephone substationinstrument adapted to be coupled to the line conductors in a telephonesystem to provide an alternat-` ing current signal output to anelectroluminescent cell on the substation instrument comprising inputmeans for coupling the power supply circuit to said line conductors,

an inverter circuit coupled to sa1d input means operative to generatealternating current output signals of a value to energize. saidelectroluminescent cell, output means for coupling saidalternating'current signals to said electroluminescent cell, andpotential storage means in said power supply circuit for supplying`auxiliary power to said inverter circuit, a charging circuit for saidpotential storage means, andmultiposition switching means on saidsubstation set operative in one position to connect a charging potentialobtained from said line conductors to said charging circuit and saidpotential storage means, and operative in a second positionV to connectsaid potential storage means to energize said inverter circuit.

13. A power supply circuit as setv forth in claim 12 in which saidmultiposition switching means includes contact means controlled bytheswitch-hook on said substation means, saidY switch-hook controlingsaid contacts to connect saidr potential storage means to said -in- 17verter circuit responsive to operation of the switch-hook preparatoryvto use of the substation instrument, and to connect said chargingpotentials to said potential storage means responsive to operation ofsaid switch-hook subsequent to use of the substation instrument.

14. A power supply circuit as set forth in claim 12 in which saidmultiposition switching means includes contact means operative with saidswitch-hook means in said one position to control said inverter means tooperate to provide a first power output, and operative in said secondposition to control said inverter means to operate to provide a poweroutput of a greater value than said irst power output.

15. In a power supply circuit adapted to be coupled to a low voltagedirect current source in a telephone system to provide an alternatingcurrent signal output to an electroluminescent cell yfor a subscribersubstation set comprising input means for coupling the power supplycircuit to the direct-current conductors of a telephone line, aninverter circuit in said substation set coupled to said input meansoperative responsive to said low voltage, directcurrent power of thetelephone system to generate alternating current output signals of `avalue to energize said electroluminescent cell, output means forcoupling said alternating current signals to said electroluminescentcell, and control means in said power supply circuit adjustable toVdiierent positions by the subscriber operative in the differentpositions to vary the value of the output signals coupled to theelectrolfuminescent cell by said inverter circuit, to thereby permitadjustment of the intensity of the yelectroluminescent cell illuminationto correspondingly different values. 16. In a power supply circuitadapted to be coupled to the low voltage, direct current subscriber lineconductors in a telephone system Ito provide an alternating currentsignal output to energize a light producing media -for a telephonesubstation set comprising input means for coupling the power supplycircuit to t-he line conductors of a telephone line, signal generatormeans including an in'verter circuit housed within said substation setcoupled to said input means operative responsive to said low voltage,direct-current potential on said subscriber line conductors of thetelephone'system to generate alternating current output signals of apredetermined frequency range, la light producing media operativeresponsive to the coupling of alternating current signals of saidfrequency range thereto, and output means for coupling said alternatingcurrent signals to said light-producing media.

17. In a power supply circuit adapted to be coupled to direct currentline conductors in a telephone system to provide an alternating currentsignal output to energize a light producing media for' a telephonesubstation set comprising input means for coupling the power supplycircuit to the line conductors of a-telephone line, signal generatormeans including an inverter circuit -for said substation set coupled tosaid input means operative responsive to said direct-current on saidline conductors to generate alternating current output signals of avalue to enertgize said light-producing media, output means Iforcoupling said alternating current signals to said light-producing media,and potential storage means in said power supply circuit operative tosupply auxiliary power to said inverter circuit to maintain t-he signaloutput of said inverter circuit at predetermined desired valuessubstantially independent of changes of potential on said 'lineconductors.

18. In a power supply circuit adapted to be coupled to the Idirectcurrent line conductors in a telephone system t-o provide power forenergizing a light producing media in a substation set comprising inputmeans for coupling the power supply circuit to the direct-current lineconductors of the telephone line, signal generator means coupled to saidinput means operative responsive to said direct current on said lineconductors to generate alternating current output signals of a value toenergize said light-producing media to provide illumination for saidsubstation set, output means for coupling said output signals to saidlight-producing media, and potential storage means connected in saidpower supply circuit to supply auxiliary power to said signal generatormeans at least at cert-ainperiods of operation of said signal generatormeans to maintain the signal output thereof at predetermined desiredvalues substantially independent of variation of the direct currentpotential on said line conductors.

19; In a power supply circuit adapted to be coupled to thedirect-current line conductors in a telephone system to provide analternating-current signal output to a lightemitting media comprisinginput means for coupling the power supply circuit to said direct-currentline conductors including means operative to couple at least a portionof the ringing current-s to said power supply circuit, said power supplycircuit comprising signal generator means including inverter meanscoupled to said input means operatively controlled -by said`direct-current power to generate alternating current output signals,the value of the output signals varying in response to the variations ofthe value ofthe ringing current :on the line, and output means forcoupling said varying alternating current signals to said light-emittingmedia to provide a pulsating light ou-tput by said media as a visualindication of the receipt of ringing signals over the line conductors.

20. In a power supply circuit for a substation' set adapted to becoupled to a set of direct current `line conductors in a telephonesystem including party lines to provide an alternating current signaloutput to energize a light producing media for its substation set, eachset of line conductors having a potential of a rst value thereonwhenever the set of line conductors are not in use, and a potential of asecond value whenever a subscriber connected to the line conductorseizes the line i or use, said power supply circuit comprising inputmeans for coupling the power supply circuit to a set of line conductors,signal generator means coupled to said input 'means operativelycontrolled by the direct current potential of said first value on saidline conductor to generate alternating currentY output signals of avalue to energize said light-producing means, and being non-operativeresponsive to said potential of said second value on said line togenerate signals of a value to energize said light-producing mediawhereby in the connection of the substation Vsets to a party line theuse of the party line by a subscriber thereon effects extinguishment ofthe lightproducing media at each of the other substations which areconnected thereto.

References Cited in the iile of this patentV UNITED STATES PATENTS2,937,298 Putkovich et al. May 17, 1960

1. IN A POWER SUPPLY CIRCUIT ADAPTED TO BE COUPLED TO THE VOICECOMMUNICATION LINES EXTENDING FROM AN EXCHANGE TO A SUBSCRIBERSUBSTATION SET IN A TELEPHONE SYSTEM TO PROVIDE AN ALTERNATING CURRENTSIGNAL OUTPUT TO AN ELECTROLUMINESCENT CELL FOR SAID SUBSCRIBERSUBSTATION SET COMPRISING INPUT MEANS FOR COUPLING THE POWER SUPPLYCIRCUIT TO SAID VOICE COMMUNICATION LINES, AN INVERTER CIRCUIT COUPLEDTO SAID INPUT MEANS INCLUDING OSCILLATOR MEANS OPERATIVE RESPONSIVE TOTHE LOW VOLTAGE, DIRECT-CURRENT POWER ON SAID VOICE COMMUNICATION LINESTO GENERATE ALTERNATING CURRENT OUTPUT SIGNALS OF A VALUE TO ENERGIZESAID ELECTROLUMINESCENT CELL, AND OUTPUT MEANS FOR COUPLING SAIDALTERNATING CURRENT SIGNALS TO SAID ELECTROLUMINESCENT CELL.